Floatplanes, by their mission profile, operate as single aircraft, while proper bomber formations are usually a flight of 3 aircraft. Given the light bomb loads of most FPs (other than the larger types such as the PBY, Sunderland, etc), their potential for causing any appreciable damage on, say, a CA or BB is minimal to nil. If, however, you do decide to use a flight of 3 Petes or SOCs as a bomber flight, then they would be considered level bombers (and expect to have them knock out of the sky as they're slow, easy targets for any AA).